This invention relates to a thin film magnetic head and more particularly to a thin film magnetic head having a multi-winding coil and a narrow gap depth, which is preferably adapted to a high density recording/reproducing.
In recent years, the high density recording in disk devices and the like has been eagerly demanded. In order to meet this demand, first, the recording density in a track width direction is increased. However, this leads to a problem of the reduction of a single reproduction output since the track width is reduced. To overcome this problem it is necessary to increase the number of windings of a conductor coil in a limited area. Further, to meet the above demand, the recording frequency is also increased to increase the line recording density. But, this also leads to the same problem. Moreover, the disk device, etc. are miniaturized. This also gives rise to the same problem since the relative speed between a recording medium and the head is reduced. Thus, now, the magnetic head having a more improved performance is required to obviate the reduction of a single reproduction output.
To prevent the reduction of a reproduction output resulting from the increase of the recording density, it is usual to give a larger coersive force to a recording medium. This requires a thin film magnetic head having such a structure as to increase the recording magnetic field. To obtain such a head, it has been proposed to increase the gap length and core thickness while decreasing the gap depth. When gap length and the core thickness are increased, however the reproduction output is inclined to be decreased in a high frequency range. This is not preferable. Thus, it is necessary to decrease the gap depth more greatly than before.
In order to prevent the reproduction signal output reduction resulting from the decrease of the relative speed between the recording medium and the magnetic head, it is also necessary to make many windings of a conductor coil in a limited area as in the case where the track width is reduced as mentioned above.
A previously known typical thin film magnetic head has eight windings of a substantially elliptical conductor coil for the purpose of a higher recording/reproduction as before. Such a thin film magnetic head is disclosed in JP-A-No. 55-840l9 corresponding to U.S. Pat. No. 4,190,872 filed in 1978 and JP-A-No. 55-84020 corresponding to U.S. Pat. No. 4,216,854 filed in 1978. However new problems posed by such a magnetic head, are not proposed in those patent applications.
The problems newly posed are follows.
In the case where many windings are wound in a single layer conductor (coil) structure in a limited area, the coil resistance is increased. To prevent this, the coil thickness must be increased and the coil intervals must be decreased. To provide the coil with an increased thickness, the photoresist used when they are formed must be also increased in its thickness. However, it is difficult to pattern the thick photoresist and so the thick coil with a high accuracy during the production process. The short-circuiting between the coil windings may frequently occur because of any alien substance mixed between the coil windings since the coil intervals are short. This leads to the reduction of a production yield of the head. Further, in the aforesaid case, the area of the region connecting the central portion of spiral windings with an external circuit must also be decreased. However, it is difficult to form such a connection region in a decreased area with less variation. Thus, the connection resistance may vary while the head is being used so that a stabilized recording/reproduction characteristic can not be provided. This is a serious problem in the reliability of the head.
One structure for making many windings of a conductor in a limited area is proposed in Japanese Patent Publication No. 49-33648. In this structure, many layers of a conductor having a wide width are stacked on a substrate through individual insulating, layers. However, a great many layers must be stacked in order to obtain a satisfactory characteristic of the head. This provides an undesired increase of the number of fabrication steps.
Another structure is a multi-layer multi-winding constructor structure as disclosed in JP-A-No. 56-8124. If the number of conductor layers is increased as in this structure, the plane where the coil windings are formed becomes higher. This makes it difficult to form the individual coil windings, with a high accuracy, on the entire surface of the substrate. Since a second magnetic member is formed at a higher step displacement portion in a subsequent step, the provision of a track width with a high accuracy is also made difficult. Further, the window within a magnetic yoke is heightened and the end point of the gap depth, which is determined by etching, at the side opposed to the medium, the insulator within the magnetic yoke, is formed with a decreased accuracy. This gives rise to the variations in the gap depth. The slope portion of the insulator on the side of the magnetic yoke is also difficult to manufacture so that it can have a predetermined angle of the slope and size between the conductor and the magnetic member because of the excess or shortage of etching. Thus, the desired recording characteristic and insulating property between the conductors and magnetic members may vary or can not be obtained. Therefore, the number of the conductor layers is required to be limited so that their many windings can be made without increasing the height of the window within the magnetic yoke.
Still another structure is a two-layer multi-winding conductor structure as shown in JP-A-No. 60-1335l6 corresponding to U.S. Pat. application Ser. No. 684,300 filed in 1984. This structure does not take into consideration the aforesaid problems and also the following problem posed when a small gap depth is intended to be provided with a high accuracy. More specifically, in order to obtain the head with a predetermined depth, the gap depth, which can be decided by machining the head surface opposed to the recording medium, must be measured through a thick protection film from the side where a head element is to be formed. Therefore, the gap depth of approx. 1 .mu.m or less is difficult to measure with a high accuracy. Namely, the small gap depth is difficult to obtain and may vary, thus making it difficult to provide a stabilized and satisfactory electro-magnetic conversion characteristic.
Further, a method of manufacturing a thin film magnetic head with a small gap depth is disclosed in JP-A-No. 61-322l2 corresponding to U.S. Pat. No. 4,749,439 filed in 1985.